Triglycerides represent the major form of energy stored in eukaryotes. Disorders or imbalances in triglyceride metabolism are implicated in the pathogenesis of and increased risk for obesity, insulin resistance syndrome and type II diabetes, nonalcoholic fatty liver disease and coronary heart disease (see, Lewis, et al, Endocrine Reviews (2002) 23:201 and Malloy and Kane, Adv. Intern. Med. (2001) 47:11 1). Additionally, hypertriglyceridemia is often an adverse consequence of cancer therapy (see, Bast, et al. Cancer Medicine, 5th Ed., (2000) B.C. Decker, Hamilton, Ontario, CA).
A key enzyme in the synthesis of triglycerides is acyl CoA:diacylglycerol acyltransferase, or DGAT. DGAT is a microsomal enzyme that is widely expressed in mammalian tissues and that catalyzes the joining of 1,2-diacylglycerol (DAG) and fatty acyl CoA to form triglycerides (TG) at the endoplasmic reticulum (reviewed in Chen and Farese, Trends Cardiovasc. Med. (2000) 10: 188 and Farese, et al, Curr. Opin. Lipidol. (2000) 11:229). It was originally thought that DGAT uniquely controlled the catalysis of the final step of acylation of diacylglycerol to triglyceride in the two major pathways for triglyceride synthesis, the glycerol phosphate and monoacylglycerol pathways. Because triglycerides are considered essential for survival, and their synthesis was thought to occur through a single mechanism, inhibition of triglyceride synthesis through inhibiting the activity of DGAT has been largely unexplored.
Genes encoding mouse DGAT1 and the related human homologs ARGP1 (human DGAT1) and ARGP2 (human ACAT2) now have been cloned and characterized (Cases, et al, Proc. Natl. Acad. Sci. (1998) 95:13018; Oelkers, et al, J. Biol. Chem. (1998) 273:26765). The gene for mouse DGAT1 has been used to create DGAT knock-out mice to better elucidate the function of the DGAT gene.
Unexpectedly, mice unable to express a functional DGAT1 enzyme (Dgat1−/− mice) are viable and still able to synthesize triglycerides, indicating that multiple catalytic mechanisms contribute to triglyceride synthesis (Smith, et al, Nature Genetics (2000) 25:87). Other enzymes that catalyze triglyceride synthesis, for example, DGAT2 and diacylglycerol transacylase, also have been identified (Cases, et al, J. Biol. Chem. (2001) 276:38870). Gene knockout studies in mice have revealed that DGAT2 plays a fundamental role in mammalian triglyceride synthesis and is required for survival. DGAT2 deficient mice are lipopenic and die soon after birth, apparently from profound reductions in substrates for energy metabolism and from impaired permeability barrier function in the skin. (Farese, et al., J. Biol. Chem. (2004) 279: 11767).
Significantly, Dgat1−/− mice are resistant to diet-induced obesity and remain lean. Even when fed a high fat diet (21% fat) Dgat1−/− mice maintain weights comparable to mice fed a regular diet (4% fat) and have lower total body triglyceride levels. The obesity resistance in Dgat1−/− mice is not due to decreased caloric intake, but the result of increased energy expenditure and decreased resistance to insulin and leptin (Smith, et al, Nature Genetics (2000) 25:87; Chen and Farese, Trends Cardiovasc. Med. (2000) 10: 188; and Chen, et al, J. Clin. Invest. (2002) 109:1049). Additionally, Dgat1−/− mice have reduced rates of triglyceride absorption (Buhman, et al, J. Biol. Chem. (2002) 277:25474). In addition to improved triglyceride metabolism, Dgat1−/− mice also have improved glucose metabolism, with lower glucose and insulin levels following a glucose load, in comparison to wild-type mice (Chen and Farese, Trends Cardiovasc. Med. (2000) 10: 188).
The finding that multiple enzymes contribute to catalyzing the synthesis of triglyceride from diacylglycerol is significant, because it presents the opportunity to modulate one catalytic mechanism of this biochemical reaction to achieve therapeutic results in an individual with minimal adverse side effects. Compounds that inhibit the conversion of diacylglycerol to triglyceride, for instance by specifically inhibiting the activity of DGAT1, will find use in lowering corporeal concentrations and absorption of triglycerides to therapeutically counteract the pathogenic effects caused by abnormal metabolism of triglycerides in obesity, insulin resistance syndrome and overt type II diabetes, congestive heart failure and atherosclerosis, and as a consequence of cancer therapy.
Because of the ever increasing prevalence of obesity, type II diabetes, heart disease and cancer in societies throughout the world, there is a pressing need in developing new therapies to effectively treat and prevent these diseases. Therefore there is an interest in developing compounds that can potently and specifically inhibit the catalytic activity of DGAT, in particular DGAT1.
We have now unexpectedly found that the compounds of the present invention exhibit DGAT inhibitory activity, in particular DGAT1 inhibitory activity, and can therefore be used to prevent or treat a disease associated with or mediated by DGAT, such as for example obesity, type II diabetes, heart disease and cancer. The compounds of the invention differ from the prior art compounds in structure, in their pharmacological activity, pharmacological potency, and/or pharmacological profile.
We have also unexpectedly found that DGAT inhibitors can be used to elevate the levels of one or more satiety hormones, in particular glucagon-like-peptide-1 (GLP-1) and therefore DGAT inhibitors, in particular DGAT1 inhibitors, can also be used to prevent or treat a disease which can benefit from elevated levels of a satiety hormone, in particular GLP-1. Glucagon-like peptide 1 (GLP-1) is an intestinal hormone which generally stimulates insulin secretion during hyperglycemia, suppresses glucagon secretion, stimulates (pro) insulin biosynthesis and decelerates gastric emptying and acid secretion. GLP-1 is secreted from L cells in the small and large bowel following the ingestion of fat and proteins. GLP-1 has been suggested, among other indications, as a possible therapeutic agent for the management of type 2 non-insulin-dependent diabetes mellitus as well as related metabolic disorders, such as obesity.
Thus, by the present finding, a disease which can benefit from elevated levels of GLP-1 can be treated with small molecules (compared to large molecules such as proteins or protein-like compounds, e.g. GLP-1 analogues).